1. Field of the Invention
This invention relates to electric heating and more particularly to metal heating by electric arc suitable for use with welding devices.
2. Description of the Prior Art
The prior art has provided a variety of welding apparatuses and control units for welding an electrode or a stud to a workpiece. The welding of a stud to a workpiece is frequently performed on a construction location requiring the welding apparatus to be portable and compact to transport. Capacitive discharge stud welding devices have incorporated solid state circuitry but heretofore the direct current welding controls have relied on a transformer-rectifier combination. The direct current output of these transformer-rectifier combinations was controlled on the secondary side of the transformer by phase controlling a D.C. output in the order of 1,200 amperes at 50 volts. In addition, a short circuit may exist between the stud and the workpiece after the welding operation depending upon whether a cold or hot plunge welding operation is used by the stud welding device. The only solid state component presently available having the capability of controlling the current on the secondary side of the transformer-rectifier combination is a thyristor. A thyristor once conducting will continue to conduct until the thyristor current is terminated by some other component in the circuit. Heretofore, thyristor circuits capable of commutating large current levels were found in motor power circuits and generally were not portable units. The prior art has failed to develop a stud welding apparatus having a thyristor controlled secondary circuit which is portable.
Therefore, an object of this invention is to provide a control for a welding device incorporating solid state circuitry to control the output current of a welding device.
Another object of this invention is to provide a control for a welding device incorporating thyristor control of the welding current with commutation means for terminating conduction of the thyristor.
Another object of this invention is to provide a control for a welding device incorporating a timer circuit for providing a plurality of timer outputs in accordance with preselected time intervals for controlling a welding sequence.
Another object of this invention is to provide a control for a welding device including a novel shunt leakage circuit for preventing a substantial electric potential difference from developing between the electrode and the workpiece.
Another object of this invention is to provide a control for a welding device incorporating a photo-electric of OPTO isolator device for connecting the low power control circuits with the high power control circuit.
Another object of this invention is to provide a control for a welding device incorporating a novel charging circuit for charging a commutating capacitor for commutating the welding current.
Another object of this invention is to provide a control for a welding device incorporating a novel commutation circuit enabling the use of an electrolytic commutating capacitor.
Another object of this invention is to provide a control for a welding device incorporating a two stage commutation circuit for commutating the welding current.
Another object of this invention is to provide a control for a welding device which results in an accurate and an adjustable control of the sequence of a welding operation.
Another object of this invention is to provide a control for a welding device which is applicable to existing said welding devices.